Surge dissipator for electrical precipitation circuits



G. R. LEWERS SURGE DISSIPATDR FOR ELECTRICAL PRECIPITATION CIRCUITS Filed May 18, 1920 IIIIIIIN anuewfoz:

Y Patented Oct. 27, 1925.

UNITED STATES I 1,558,991 PATENT OFFICE}.

GEORGE R. LEWERS, OF NEW YORK, N. Y., ASSIGNOR TO RESEARCH CORPORATION, OI

' NEW YORK, N. Y., A CORPORATION OF NEW YORK.

S URGE DISSIPATOR FOR ELECTRICAL PRECIPITATION CIRCUITS.

Application filed May 18, 1920. Serial No. 382,328.

To all whom it may concern:

Be it known that I, GEORGE R. Lnwnns, a citizen of the United States, residing at 11 South Portland Avenue, Brooklyn, New York, in the county of Kings and State of New York, have invented certain new and useful Improvements in Surge Dissipators for Electrical Precipitation Circuits, of which the following is a specification.

The purpose of this invention is to provide means for dissipating surges that may be set up in electrical precipitator circuits in an improved manner, which is automatic in operation and which functions with a minimum of electrical disturbances.

The particular purpose of this invention is to employ a corona discharge in parallel with the electrical circuit of an electrical precipitator for the purpose of maintaining steady conditions in the circuit and so realize a high efiiciency of the precipitator.

That steady conditions must exist in an electrical precipitator circuit in order to obtain smooth operation of the precipitator and constant cleaning of the gases is well known, but although persistent attempts have been made to assure these desired conditions, satisfactory results have seldom been consistently realized. It has been previously known that the energy in the peaks of surges can be dissipated through air or other gas as corona discharge, but no one has previously applied this principle to electrical precipitators for the purpose of dissipating surges therein because it was always assumed that the corona discharge within the precipitator itself would automatically dissipate surges in this manner if they could be so dissipated. But it must be realized that particular conditions exist within electrical precipitators. The gases, especially those arising from metallurgical operations, have electrical characteristics that difler greatly from air; the suspended particles they contain influence these characteristics, and temperature, pressure and moisture content are all factors to be considered. It is evident, therefore, that the efi'ect a corona discharge may have upon acircuit depends upon the medium through which the discharge takes place.

The gases treated in an electrical precipitator may be such that the energy passed through or into them as corona discharge 1s relatively small. Also as the suspended material collects upon the electrodes it may decrease the discharge still further; especially is this so if the material is a non-conductor of electricity. \Vhen such conditions exist precipitation of the suspended material is not fully realized and results in attempts being made to raise the voltage and increase the efficiency of recovery. Disruptive sparkover follows the rise in voltage and surges are set up in the electrical circuit. Now if the gases being treated were good conductors of electricity and there were no non-conduct ing deposit on the electrodes to prevent the passage of current, disruptive sparkover would probably not take place, or if there were a tendency for sparkover it would be dissipated as it progresses within the precipitator. But as we have seen conditions are not always so favorable and dissipating means without the precipitator are necessary. Corona discharge apparatus properly placed in parallel with the high voltage line connecting the precipitator to the source of high voltage current has been found very beneficial in this regard.

It is sometimes necessary to run a long transmission line between the electrical apparatus and the precipitator and this intensifies the tendency of the circuit to surge. The capacity and inductive reactance of the circuit may hear such relation at times of surges when the frequency is high, that a condition of resonance is approached, and the point of resonance, (the point where the voltage reaches a maximum) may be somewhere along the transmission hne. Ifth1s point can be determined it is advisable to place a properly proportioned and spaced corona apparatus there.

Experience with a particular problem will dictate the form of apparatus best sulted to that problem and the method of using 1t. Types of apparatus which give good results and the method of using same are illustrated in the accompanying drawings. Fig. 1 is a diagrammatic view of typlcal electrical precipitation circuit. Fig. 2 1s a detail side view of the particular apparatus used in the circuit shown in Figure l for accomplishin the purpose of the invention. Fig. 3 is a si e view of another form of this apparatus. Fig. 4 is a side view of an apparatus similar to that in Figure 3, but connected up in a sli htly different manner. Figs. 5 and 6 are si e views of still different forms of this apparatus, and Figure 7 shows a modification.

In Fig. 1 the low-tension circuit including the generator 1 and the primary transformer coil 2 and the load circuit includmg the secondary transformer coil 3, the rectifier 4 and the precipitator 5 are the usual ele: ments of a typical electric precipitation c1rcuit, 5' being the collecting electrode casing, 5" the discharge electrode system and 6 a bushing through which transmission line 4 enters the precipitator.

Into the transmission line 4 is placed an apparatus which embodies the invention. This apparatus includes a discharge o1nt 7 supported by a bracket and electrically connected to the transmission line. The bracket in turn is supported u on an insulator 8. The discharge point is directed against a grounded plate 9 supported in spaced relation thereto.

The apparatus just described represents one form'of corona inducing devices available for the purposes of the invention. As more clearly shown in Fig. 2, the polnt 7 may be adjustably secured by means of lock nuts 7 By turning the thumb nut 10 the distance between the point 7 and the plate 9 may be adjusted to suit particular conditions of voltage and gas to be treated.

In Fig. 3, 11 represents acylinder of conducting material through which extends a discharge rod or wire 12 supported'between insulators 13. Wire 12 forms part of the load circuit and the cylinder 11, which is mounted upon supports 14, is connected'to ground. i

Fig. 4 shows an arrangementsimilar to that disclosed in Fig. 3, but the rod or wire 15 is in parallel with the transmission line 4, while in Fig. 3- the wire 12 is in series therewith.

Fig. 5 shows apparatus especially adapted for inducing a very heavy corona discharge and the'discharge electrode consists of a prong-covered cylinder 16 within the screen cylinder 17. The apparatus need not be of the cylindrical type, however, but can be made of flat electrodes as shown in Fig. 6, where 18 represents the grounded electrode made of wire screen and 19 is a flat plate or screen from which the points 20 project.

It is of. course understood that the corona device may be employed in conjunction with other devices tending to.eliminate surges or reduce their amplitudes. One example is shown in Fig. 7 where 21 represents an inductance coil, preferably of relatively'low reslstance, in-series with the transmission line and 22 is a corona device such as shown in Fig. 1. During normal operation of the preclpitation circuit the potential difference between the endsof the coil 21 is small.

As soon, however, as due to resonance or othern conditions,"the voltage of the circuit is raised, the electric energy thus set free is dissipated through the corona device While it is possible to arrange the apparatus so that no discharge takes place at normal voltages, it has been found that a corona discharge continuously in parallel with a circuit maintains steady and satisfactory conditions therein, with the result that the operation .of the precipitator is maintained at high efliciency. The amount of energy dissipated by the corona at normal voltages should not be greatcenough to be a'serious factor in the current consumption of the precipitator. From 1% to 10% of the total energy in the circuit may be so dissipated. The number of points required to give this corona must be determined for each particular case, although it has been found that for most installations a single point gives sufiicient efl'ect. At times of surges when the voltage becomes excessive, the corona will be found to magnify greatly and approach disruptive conditions. The spacing should be such that disruptive sparkover takes place only when the voltage is high enough to endanger the transformer and other electrical apparatus.

It has been found that a corona discharge remains steady when the gaseous medium employed is highly humidified air. It is therefore recommended that at times when the atmospheric conditions are not favorable in this respect artificial humidification be resorted to. In fact, the whole surge dissipation apparatus can be placed in a chamber containing air of high humidity or some other gas suitable for the purpose set forth.

One method of accomplishing this result is to inject through inlet 24, Fig. 3, humidified air.

As is well known, a negative corona gives the most satisfactory. results in an electrical precipitator, and fortunately the apparatus described will work best when the discharge point is negative. In fact, the distance between electrodes when most suitable for negative corona, is entirely toolsmall when positive corona is placed on the discharge point. This being the case, it can readily be seen how this apparatus can be used as a polarity indicater, because if .set for a negative corona it will immediately spark over when for any reason positive corona should be present.

I claim: I 1. In combination with an electric circuit ncludlng an electric precipitator, of means n parallel with the precipitator for effectmg a corona discharge, said means being constructed and arranged to maintain a corona discharge at the normal operating voltage of the precipitator.

2. In combination with an electric precipitator and a circuit for feeding unidirectional current to the dischar e electrode thereof; of means in parallel with the recipitator constructed and arranged to e ect a corona dischar e at the normal operating voltage, the sai means including an element having a relatively large and smooth superficial area, connected to have substantially the potential of the collecting electrode of the precipitator and means whereby the corona discharge is efiected from a part of the circuit having substantially the potential of the discharge electrode of the precipitator to the said element. 1

3. Apparatus according to claim 2 in which the said element is cylindrical and the means for effecting the corona discharge is a'fine wire connected with'the circuit and extending through the cylindrical element.

In testimony whereof, I aflix my signature.

GEORGE R. LEWERS. 

